I say stay with your boyfriend. But you can do whatever you want, it's your life :)
So Im in a 3 year long relationship and ive recently developed feelings for another guy what do I do?
Well you have to make a grown up decision ..
There are a few things to ponder
1) Do you want to be in a relationship
2) Do you 'love' this guy your are in a relationship with enough to be monogomous
3) Are you too young and uncommited to even BE in a relationship
4) Is the guy you are "with" deserving of having a partner who is NOT commited on a level where she even contemplates 'being with someone else'